As was discussed in the background of U.S. Pat. No. 4,641,676, portable shelters have been in existence since prehistoric time, but modern times have seen an increasing need for greater sophistication in the quality and type of construction in portable shelter apparatus. In the last 20 years, this industry has dramatically grown as a result of new techonologies in fabrics, support structure and design, especially in the fields of lightweight tents and mountaineering shelters. These developments manifest themselves in special application fields, but relatively little attention has been paid to the development of larger area shelters that are stored in a small collapsed state but which may be expanded with a minimum amount of effort into sturdy, large area shelters.
One response to this need is shown in my U.S. Pat. No. 4,641,676. This patent shows a portable canopy structure having a framework that may be collapsed into a stored state yet which may be expanded and erected for use. The framework includes a plurality of upright support members which are interconnected by a plurality of scissor assemblies; an internal scissor assembly is provided to support a central post, and a covering extends across the tops of the supports and is supported thereon in a dome-like manner. This structure is also similar to that described in U.S. Pat. No. 4,607,656 issued 26 Aug. 1986, to Carter.
While the structure shown in the Lynch patent and the Carter patent provides significant advantages over the earlier prior art noted above, especially in the relative ease of both expansion and collapse, they nonetheless have some drawbacks. For example, in use, the scissor assemblies shown in these two structures are under compressive forces. When the scissor assemblies are subjected to forces transversely of their plane, the combination of this force with the compressive force can result in substantial bowing of the scissor assemblies and distortion of the canopy framework. Additionally, the use of a central scissor assembly extending across the middle of the framework can be inconvenient in reducing the head room provided for persons sheltered by the canopy structure.
In addition to the structure shown in the Lynch patent and the Carter patent described above, other prior art structures have been developed to provide temporary shelters. For example, French Patent No. 823,693 issued to Boeuf and published 25 Jan. 1938 shows a framework for supporting a shelter wherein the framework has a plurality of upright posts which are interconnected by single scissor assemblies. A plurality of roof support elements are then bolted to each upright posts and are then secured together by means of a central wing-nut assembly to define a peak for the framework. U.S. Pat. No. 2,928,404 discloses a collapsible shelter wherein upright posts pivotally secure rigid roof support elements so that the structure may fold together.
Accordingly, despite the advances of the abovedecsribed canopy structures, there remains a need for further improved canopy structure which provides a quick erectable temporary shelter which is easy to expand for use and to collapse for storage in a fast, efficient manner. There is a further need for such an improved canopy structure which increases the mechanical strength of the framework and which provides greater head room thereby more efficiently using space.